U.S. patent application number 11/359745 was filed with the patent office on 2007-08-23 for automatic gain control system for receivers in wireless communications.
This patent application is currently assigned to Nokia Corporation. Invention is credited to Qizheng Gu.
Application Number | 20070197178 11/359745 |
Document ID | / |
Family ID | 38428868 |
Filed Date | 2007-08-23 |
United States Patent
Application |
20070197178 |
Kind Code |
A1 |
Gu; Qizheng |
August 23, 2007 |
Automatic gain control system for receivers in wireless
communications
Abstract
An AGC system in a receiver adjusts the front-end gain not only
based on the received sector power level, but also based on the
strength of the present interference. When there is no presence of
strong electromagnetic interference, the front-end gain of the
receiver is set at a high level so that the receiver is maintained
at a high sensitivity level. The receiver is operable at a normal
current mode and a current saving mode. The receiver is set to run
at the normal mode when the received sector power is lower than a
certain predetermined level or when a strong interference is
present.
Inventors: |
Gu; Qizheng; (San Diego,
CA) |
Correspondence
Address: |
WARE FRESSOLA VAN DER SLUYS &ADOLPHSON, LLP
BRADFORD GREEN, BUILDING 5
755 MAIN STREET, P O BOX 224
MONROE
CT
06468
US
|
Assignee: |
Nokia Corporation
|
Family ID: |
38428868 |
Appl. No.: |
11/359745 |
Filed: |
February 21, 2006 |
Current U.S.
Class: |
455/232.1 |
Current CPC
Class: |
H03G 11/002
20130101 |
Class at
Publication: |
455/232.1 |
International
Class: |
H04B 1/06 20060101
H04B001/06; H04B 7/00 20060101 H04B007/00 |
Claims
1. A method to adjust a gain in an RF front-end of a wireless
communications device having a receiver for receiving communication
signals, the received signals having a measured power level,
wherein the communication signals are subject to an electromagnetic
interference affecting the received signals, said method comprising
the steps of: detecting the interference for determining an
interference level; setting the gain at a first gain level if the
measured power level is equal to or higher than a predetermined
level; and setting the gain at a second gain level higher than the
first gain level if the measured power level is lower than the
predetermined level, wherein when the measured power level is lower
than the predetermined level and the determined interference level
is higher than a predetermined interference value, reducing the
gain to a third level lower than the second gain level.
2. The method of claim 1, wherein the third level is substantially
equal to the first gain level.
3. The method of claim 1, wherein the receiver is operable at a
first current mode and a second current mode, wherein the first
current mode defines a higher receiver current level and the second
current mode defines a lower received current level, said method
further comprising the step of: operating the receiver at the first
current mode when the measured power level is lower than a further
power level lower than the predetermined level.
4. The method of claim 3, further comprising the steps of:
operating the receiver at the second current mode when the measured
power level is equal to or higher than the further power level; and
increasing the receiver current level to a level higher than the
lower receiver current level, when the determined interference
level is greater than a predetermined interference value.
5. The method of claim 4, wherein the increased receiver current
level is substantially equal to the higher receiver current
level.
6. The method of claim 3, further comprising the step of: operating
the receiver at the first current mode if the measured power level
is equal to or higher than a predetermined level and the determined
interference level is higher than the predetermined interference
level.
7. The method of claim 2, further comprising the step of: setting
the gain at a fourth level higher than the second level if the
measured power level is lower than the further power level, but if
the determined interference level is greater than a further
interference value, reducing the gain level to the second gain
level.
8. The method of claim 7, wherein the receiver is operable at a
first current mode and a second current mode, wherein the first
current mode defines a higher receiver current level and the second
current mode defines a lower receiver current level, said method
further comprising the step of: operating the receiver at the first
current mode when the measured power level is lower than a third
power level lower than the further power level.
9. The method of claim 8, further comprising the steps of:
operating the receiver at the second current mode when the measured
power level is equal to or higher than the third power level; and
increasing the receiver current level to a level higher than the
lower receiver current level, when the determined interference
level is greater than a further interference value.
10. The method of claim 8, further comprising the steps of:
operating the receiver at the second current mode when the measured
power level is equal to or higher than the further power level; and
increasing the receiver current level to a level higher than the
lower receiver current level, when the determined interference
level is greater than a predetermined value.
11. An automatic gain control system for adjusting a gain in an RF
front-end of a wireless communications device, the wireless
communications device having a receiver for receiving communication
signals, the received signals having a measured power level,
wherein the communication signals are subject to an electromagnetic
interference affecting the received signals, said system
comprising: a gain controller for setting the gain at a first gain
level if the measured power level is equal to or higher than a
predetermined level; and setting the gain at a second gain level
higher than the first gain level if the measured power level is
lower than the predetermined level; and an electromagnetic
interference detector for determining an interference level, such
that when the measured power level is lower than the predetermined
level and the determined interference level is higher than a
predetermined interference value, reducing the gain to a first
level lower than the second gain level.
12. The automatic gain control system of claim 11, wherein the
receiver is operable at a first current mode and a second current
mode, wherein the first current mode defines a higher receiver
current level and the second current mode defines a lower received
current level, said control system further comprising: a current
mode control module, responsive to the measured power level, for
setting the receiver current level according to the first current
mode when the measured power level is lower than a further value
lower than the predetermined value and setting the receiver current
level according to the second current mode when the measured power
level is equal to or higher than the further value.
13. The control system of claim 12, wherein the current mode
control module sets the receiver current level according to the
second current mode when the measured power level is equal to or
higher than the further power level, but when the determined
interference level is greater than a predetermined interference
value, the receiver current is set according to the first current
mode.
14. The control system of claim 12, wherein the gain controller
sets the gain at a third level higher than the second level if the
measured power level is lower than the further power level, but if
the determined interference level is greater than a further
interference value, reducing the gain level to the second gain
level.
15. The control system of claim 14, wherein the receiver is
operable at a first current mode and a second current mode, wherein
the first current mode defines a higher receiver current level and
the second current mode defines a lower receiver current level,
said control system further comprising: a current mode control
module, responsive to the measured power level, for setting the
receiver current level according to the first current mode when the
measured power level is lower than a third power level lower than
the further power level.
16. The control system of claim 15, wherein the current mode
control module sets the receiver current level according to the
second current mode when the measured power level is equal to or
higher than the third power level, but when the determined
interference level is greater than a further interference value,
the receiver current level is set according to the first current
mode.
17. The control system of claim 15, wherein when the measured power
level is equal to or higher than the further power level, the
receiver current level is set according to the second current mode,
but when the determined interference level is greater than a
predetermined value, the receiver current level is set according to
the first current mode.
18. An RF receiver of a wireless communications device having an RF
front-end for receiving communication signals, wherein the
communication signals are subject to an electromagnetic
interference affecting the received signals, said RF receiver
comprising: a frequency down converter module in the RF front-end,
responsive to the received communication signals, for providing
analog base-band signals; means, responsive to the analog base-band
signals, for measuring a signal power level; a gain controller for
setting a gain of RF front-end at a first gain level if the
measured signal power level is equal to or higher than a
predetermined, and setting the gain at a second gain level higher
than the first gain level if the measured signal power level is
lower than the predetermined level; and an electromagnetic
interference detector for determining an interference level, such
that when the measured signal power level is lower than the
predetermined level and the determined interference level is higher
than a predetermined interference value, reducing the gain to a
first level lower than the second gain level.
19. The receiver of claim 18, wherein the receiver is operable at a
first current mode and a second current mode, wherein the first
current mode defines a higher receiver current level and the second
current mode defines a lower received current level, said receiver
comprising: a current mode control module, responsive to the
measured signal power level, for setting the receiver current level
according to the first current mode when the measured signal power
level is lower than a further value lower than the predetermined
value and setting the receiver current level according to the
second current mode when the measured signal power level is equal
to or higher than the further value.
20. The receiver of claim 19, wherein the current mode control
module sets the receiver current level according to the second
current mode when the measured signal power level is equal to or
higher than the further power level, but when the determined
interference level is greater than a predetermined interference
value, the receiver current is set according to the first current
mode.
21. The receiver of claim 19, wherein the gain controller sets the
gain at a third level higher than the second level if the measured
signal power level is lower than the further power level, but if
the determined interference level is greater than a further
interference value, reducing the gain level to the second gain
level.
22. The receiver of claim 21, wherein the receiver is operable at a
first current mode and a second current mode, wherein the first
current mode defines a higher receiver current level and the second
current mode defines a lower received current level, said receiver
further comprising: a current mode control module, responsive to
the measured signal power level, for setting the receiver current
level according to the first current mode when the measured signal
power level is lower than a third power level lower than the
further power level.
23. The receiver of claim 22, wherein the current mode control
module sets the receiver current level according to the second
current mode when the measured signal power level is equal to or
higher than the third power level, but when the determined
interference level is greater than a further interference value,
the receiver current level is set according to the first current
mode.
24. The receiver of claim 22, wherein when the measured signal
power level is equal to or higher than the further power level, the
receiver current level is set according to the second current mode,
but when the determined interference level is greater than a
predetermined value, the receiver current level is set according to
the first current mode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a receiver in a
wireless communications system and, more particularly, to an
automatic gain control circuit for use in the receiver.
BACKGROUND OF THE INVENTION
[0002] An automatic gain control (AGC) circuit is commonly used in
a receiver to adjust received signals to a desired reference level
before the signals are further processed by the receiver.
Conventionally, an RF receiver AGC system controls its front-end
gain based on the received sector power level only. The front-end
gain is switched at assigned sector power levels, which are derived
based on the strength of possible interference sources. Usually,
this is done without regard to the actual presence of those
interference sources. As such, the receiver sensitivity is usually
reduced after the front-end gain steps down. In order to achieve
acceptable linearity, the receiver generally runs at a relatively
high current mode.
SUMMARY OF THE INVENTION
[0003] The AGC system, according to the present invention, adjusts
the front-end gain not only based on the received sector power
level, but also based on the strength of the present interference.
When there is no presence of strong electromagnetic interference,
the front-end gain of the receiver is set at a high level so that
the receiver is maintained at a high sensitivity level or a lower
receiver noise figure. When a strong electromagnetic interference
is detected, the gain is reduced. Preferably, when a received
sector power level (as measured by RSSI, for example) is lower than
-82 dBm, for example in the CDMA mobile station case, the gain is
set to high. If a strong interference, such as an interference
stronger than -35 dBm, is detected, an interference level detector
(IDL) flag is set to ON and the gain is reduced to a predetermined
lower level. When the received sector power is higher than -82 dBm,
the gain can be set to low and remains unchanged even when a strong
interference is detected. Furthermore, if the receiver is operable
at a normal current mode and a current saving mode, the receiver is
set to run at the normal mode when the received sector power is
lower than -98 dBm, for example. When the received sector power is
equal to or higher than -98 dBm, the receiver runs at the current
saving mode unless a strong interference is present.
[0004] Thus, the first aspect of the present invention is an
automatic gain control system for adjusting the gain of an RF
front-end of a wireless communications device. The second aspect of
the present invention is a method for controlling such gain. The
third aspect of the present invention is a receiver in a wireless
communication device having such an automatic gain control system.
The automatic gain control system comprises:
[0005] an interferer level detector for determining an interference
level;
[0006] a gain controller for setting the gain at a first gain level
if the received sector power level is equal to or higher than a
predetermined level, and setting the gain at a second gain level
higher than the first gain level if the received sector power level
is lower than the predetermined level, but when the interference
level is higher than a predetermined interference value, reducing
the gain to a third level lower than the second gain level.
[0007] The third level can be substantially equal to the first gain
level, for example.
[0008] The system also comprises a current mode control module,
responsive to the received sector power level, for setting the
current level according to a higher current mode when the received
sector power level is lower than a further level lower than the
predetermined level, and setting the current level according to a
lower current mode when the received sector power level is equal to
or higher than the further level. When the received sector power
level is equal to or higher than the further level and the
interference level is greater than a predetermined interference
value, the current level is increased to a higher level.
[0009] In a different embodiment of the present invention, the
front-end can be set a high gain level, a mid gain level and a low
gain level. The front-end is set at the high gain level when the
receiver sector power level is lower than a first predetermined
level, such as -85 dBm and the determined interference level is
smaller than -35 dBm, for example. The front-end is set at the mid
gain level when the receiver sector power level is lower than the
first predetermined level and the determined interference level is
greater than -35 dBm, for example. The front-end is also set at the
mid gain level when the receiver sector power level is between the
first predetermined level and a second predetermined level, such as
-35 dBm and the determined interference level is smaller than -24
dBm, for example. Otherwise, the receiver is set to the low gain
level.
[0010] The AGC system, according to the present invention, is able
to maintain high receiver sensitivity in any possible condition as
long as the interferers are not strong enough. Furthermore, because
the receiver current is able to maintain at a current saving mode
as long as the received sector power exceeds a predetermined level
and the interferers are not strong enough. Thus, the AGC system
also improves the receiver current consumption.
[0011] The present invention will become apparent upon reading the
description taken in conjunction with FIGS. 1 to 5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram of a receiver having an AGC
system, according to the present invention.
[0013] FIG. 2 is shows the front-end gain and the receiver current
control as plotted against the received sector power in the AGC,
according to the present invention.
[0014] FIG. 3 is a state chart showing the receiver current mode
and the front-end gain of an AGC system with two front-end gain
modes, according to the present invention.
[0015] FIG. 4 is a state chart showing the receiver current mode
and the front-end gain of an AGC system with three front-end gain
modes, according to the present invention.
[0016] FIG. 5 is a schematic representation of a mobile terminal
having a receiver, according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] An RF receiver automatic gain control (AGC) system,
according to the present invention, controls its front-end gain
based on the presence of strong electromagnetic interference and
the received sector power. When there is no presence of strong
electromagnetic interference, the front-end gain of the receiver is
set at a high level. As such, the receiver can be maintained at a
high sensitivity level or a lower receiver noise figure in a broad
dynamic range between 25 and 40 dB. Preferably, the receiver is
operated at a current saving (CS) mode if such a mode is available.
When a strong electromagnetic interference is detected, the gain is
reduced. Preferably, the gain is switched to a predetermined lower
gain level and the receiver is operated at a normal current mode,
instead of the CS mode.
[0018] The receiver AGC system, according to the present invention,
is explained in terms of a code-division multiple access (CDMA)
receiver in a mobile terminal. However, the AGC system and its
principle are applicable to other receivers as well. Furthermore,
it is assumed that the receiver is at least operable at two current
modes: a normal mode and a current saving (CS) mode. When the
receiver is operated at the CS mode, it is assumed that the
receiver has substantially the same sensitivity as when the
receiver is operated in normal current consumption.
[0019] An exemplary CDMA mobile receiver, according to the present
invention, is shown in FIG. 1. The receiver, as shown in FIG. 1, is
a direct conversion receiver (DCR) with an interferer level
detector (ILD). As shown, the receiver 1 comprises two sections: an
RF analog section 100 and a digital base-band (BB) section 200. The
RF analog section 100 comprises a duplexer 20 operatively connected
to an antenna 10, and a low noise amplifier (LNA) 130 for receiving
RF signals from the duplexer 20. After the received signals are
filtered by a passband filter 132, they are
frequency-down-converted by two quadrature mixers or demodulators
150a and 150b, which separately provides I and Q analog base-band
signals 250a and 250b. As shown, an RF local oscillator (LO)
generator 140 and a phase shifter 152 are used to provide the RF LO
signals for down-conversion. The I and Q analog base-band signals
are weakly coupled to an interferer level detector (ILD) 162 for
electromagnetic interference detection. When the ILD 162 detects a
strong interference exceeding -35 dBm, for example, it sets the
flag 164 to ON. Otherwise the flag 164 is set to OFF.
[0020] The I and Q base-band signals are separately amplified by
base-band amplifiers 160a, 160b; filtered by low-pass filters
(LPFs) 170a, 170b; and amplified by variable gain amplifiers (VGAs)
180a, 180b in the I and Q channels. In the digital base-band
section 200 of the AGC system of the present invention, only a
control module 210 having a receiver AGC algorithm 212, a current
mode control sub-module 213 and a received signal strength
indicator (RSSI) 214 is shown. In order to adjust the front-end
gain, a front-end gain control signal 222 is provided to the LNA
130. Likewise, a back-end gain control signal 220 is provided to
the VGAs 180a, 180b. The gain control signals 220, 222 are provided
based on the flag 164 from the ILD 162 and the received sector
power as measured by the RSSI 214 in the digital base-band section
200. The control module 210 can also be used for controlling the
current consumption in the RF analog section 100. For example, the
control module 210 can provide a current mode control signal 230 to
various components in the RF analog section 100, based on the
received interference strength and the sector power, in order to
operate the receiver RF front-end at a normal current mode or at a
current saving (CS) mode.
[0021] The cases that the front-end gain, i.e., the LNA 130 stage
gain of the receiver architecture as shown in FIG. 1 is adjustable
only and the back-end gain is fixed, are discussed. It is assumed
that the front-end gain change is the result of the LNA gain
stepping up or down. For illustration purposes, the LNA has only
tow gain modes, a high gain mode and a low gain mode. It is
possible to achieve the LNA low gain mode by bypassing the LNA.
[0022] The receiver 1 can be operated as follows: [0023] 1. When
the receiver is turned on or wakes up from the sleep mode, the LNA
130 is first operated at its high gain mode in order to maintain a
high receiver sensitivity and the LNA is also operated at the
normal current mode. The receiver stays at the high LNA gain mode
if no strong interferer, such as that having an interference level
of -35 dBm or higher, is detected by the ILD 162. In this
situation, the flag 164 is set to OFF. Moreover, the receiver
current keeps running at the normal mode as long as the received
sector power as measured by the received signal strength indicator
(RSSI) 214, for example, is lower than -98 dBm. [0024] 2. When the
received sector power is equal to or higher than -98 dBm and there
is no presence of a strong interferer (-35 dBm or higher), the LNA
stays at the high gain mode and the current mode control signal 230
sets the receiver to a current saving (CS) mode. [0025] 3. If the
received sector power is equal to or higher than -98 dB and a
strong interferer (-35 dBm or higher) is detected, the receiver
comes back to the normal current mode in response to the current
mode control signal 230. At the same time, the front-end gain steps
down to the low gain mode, in response to the front-end control
signal 222, in order to achieve high linearity. [0026] 4. The gain
at the LNA 130 stage is normally switched to the low gain mode when
the received sector power is -82 dBm or higher even when there is
no presence of a strong interferer. However, the current mode
control signal 230 is set based on whether the flag 164 is ON or
OFF. When the received sector power reaches -60 dBm or higher, for
example, the receiver is always operated at the CS mode. Thus, when
the received sector power is between -98 dBm and -60 dBm, the
current mode is conditioned upon the presence of a strong
interferer. In this received sector power range, the receiver is
operated at the CS mode unless a strong interferer is detected.
[0027] The front-end gain and the receiver current mode of the AGC
system, according to present invention, are shown in the plot of
FIG. 2. For illustration purposes, the plot only shows the
direction of an increasing received sector power. [0028] 1. In the
region of received sector power being lower than -98 dBm, the
front-end gain is always high and the receiver is operated at the
normal current mode. [0029] 2. In the region of received sector
power between -98 dBm and -82 dBm, the front-end gain is high but
the receiver is operated at a CS mode if no strong interference is
detected. [0030] 3. In the same region, if a strong interferer is
detected by the ILD and the flag 164 (see FIG. 1) is set to ON, the
front-end gain turns to low and the receiver operates at the normal
current mode. [0031] 4. After the strong interferer is gone and the
flag 164 is set to OFF, the front-end gain resumes its high level
and the receiver again operates at the CS mode. [0032] 5. When the
received sector power is higher than -82 dBm, the front-end gain is
switched to low regardless of the presence of strong interferers.
[0033] 6. In the region of received sector power between -82 dBm
and -60 dBm, the receiver is normally operated at the CS mode
unless a strong interferer is detected. Thus, the receiver is
operated at the normal current mode only when the flag 164 is ON.
[0034] 7. When the receiver sector power is beyond -60 dBm, the
receiver is always operated at the CS current mode regardless of
the presence of strong interferers.
[0035] The state chart of the AGC system with only two front-end
gain modes (high gain mode and low gain mode), according to the
present invention, is depicted in FIG. 3. As shown in the state
chart, there are five different operations states concerning the
front-end gain and the receiver current mode. [0036] Initially, the
receiver is at the initial state 301 where the front-end gain is
high and the receiver current mode is normal. [0037] When the
received sector power as measured by RSSI 214 is between -98 dBm
and -82 dBm, the AGC is at state 303. At this state, the front-end
gain is high and the receiver current is at the CS mode. [0038]
When the received sector power is lower than -82 dBm and the ILD
flag is ON, the AGC is at state 304. At this state, the front-end
gain is low and the receiver current mode is normal. [0039] When
the received power sector is between -82 dBm and -60 dBm, the AGC
is at state 305. At this state, the front-end gain is low and the
receiver current is at the CS mode. [0040] Finally, when the
received power sector is between -82 dBm and -60 dBm and the ILD
flag is ON, the AGC is at state 306 where the front-end gain is low
and the receiver current mode is normal.
[0041] To further improve the receiver performance, the LNA 130
(see FIG. 1) can be designed with three gain modes. As such, the
LNA 130 also has a mid-gain mode between the high and low gain
modes. With the mid-gain mode, the receiver sensitivity is better
than that when it is operated at the low gain mode by bypassing the
LNA 130. For example, the LNA can be designed to make a CDMA mobile
receiver to have a -109 dBm sensitivity at the LNA high gain mode.
At the mid-gain mode, the sensitivity of the receiver is about 5 to
6 dB lower than the high-gain mode. Thus, the receiver sensitivity
is about -104 to -103 dBm. However, the linearity of the receiver
is better at the mid-gain mode than at the high-gain mode.
[0042] In order to improve the CDMA mobile receiver overall
performance, it is preferable that the receiver operates at its
mid-gain mode most of the time. A state chart illustrating the AGC
system with three front-end gain modes (high, mid and low) is shown
in FIG. 4. [0043] When the receiver is turned on, the receiver is
at its initial state (401) where the LNA is at the high gain mode
and the receiver current is at the normal mode. The AGC stays with
this state as long as the received sector power, RSSI, is lower
than -98 dBm. [0044] Depending upon the measured received sector
power (RSSI 214) level, the state transits to a different state 403
or 407. As shown, if the received sector power is between -98 dBm
and -82 dBm, the front-end gain is high but the receiver operates
at the CS mode (state 403). If the received sector power is between
-82 dBm and -35 dBm, the front-end gain is at the mid-gain mode and
the receiver operates at the CS mode, with the ILD 162 (see FIG. 1)
disabled (state 407). [0045] If the AGC is at state 403 and the
detected interferer level is equal to or higher than -35 dBm, then
the AGC goes to state 404 from 403. The state will move back to 403
when the interferer level becomes lower than -35 dBm. [0046] When
the received sector power is equal to -85 dBm or higher, the AGC
state transits to state 405 where the front-end gain is at the mid
gain mode and the receiver operates at the CS mode. If the detected
interferer level is equal to or greater than -24 dBm, the state
progresses to state 406 where the front-end gain is low and the
receiver current is normal. When the detected interferer level
reduces to a level lower than -24 dBm, the state will move back to
405 from 406. [0047] State (405) may transit to state 407 where the
front-end gain is low and current is at the CS mode with ILD
disabled, when the received sector power is equal to or greater
than -35 dBm. The state will move back to 405 from 407 if the
sector power RSSI <-35 dBm. [0048] The AGC stays at state 407 as
long as the received sector power is higher than -35 dBm.
[0049] The AGC system with two or three LNA gain modes, according
to the present invention, can be used in a CDMA mobile receiver as
illustrated above. It should be noted that the same system can also
be used in other receivers such as a time-division multiple access
(TDMA) mobile receiver, a frequency-division multiple access (FDMA)
system and the like. A mobile terminal having an AGC, according to
the present invention, is illustrated in FIG. 5. As shown, the
mobile terminal 600 comprises an upper housing part 620 and a lower
housing part 630 to accommodate various mobile phone components. As
shown, the mobile terminal 600 has a display 640 disposed on the
upper housing part 620, and a circuit board 12 disposed between the
upper and lower housing parts. The circuit board 12 has a ground
plane 14 operatively connected to an antenna 10. The antenna 10 is
operatively connected to a duplexer 20. The duplexer is operatively
connected to a front-end module 16 and another signal processor 18.
The front-end module 16 comprises a receiver 1 having the AGC
system, according to the present invention. The AGC system may be
operated at the two gain modes or at multiple gain modes.
[0050] In sum, the present invention provides an automatic gain
control system and method for controlling the gain of an RF
front-end of a wireless communications device, the communications
device having a received signal strength indicator for providing a
received sector power level. The system comprises an interferer
level detector for determining an interference level, and a gain
controller for setting the gain to low if the received sector power
level is equal to or higher than a predetermined value, and setting
the gain to high if the received sector power level is lower than
the predetermined value. But when a strong interferer is present,
the gain is reduced from high to low. As such, the AGC system,
according to the present invention, is able to maintain high
receiver sensitivity in any possible condition as long as the
interferers are not strong enough. Furthermore, because the
receiver current is able to maintain at a current saving mode as
long as he received sector power exceeds a predetermined level and
the interferers are not strong enough. Thus, the AGC system also
improves the receiver current consumption.
[0051] It should be appreciated by persons skilled in the art that
the numerical values of the received sector power and the detected
interference level are for illustration purposes only. The received
sector power and the detected interference level can be higher or
lower.
[0052] Although a CDMA mobile station receiver has been used to
illustrate the principle of the present invention, the system and
method for automatic gain control, according to the present
invention, can be used for the receivers in different protocol
wireless systems. Thus, the triggered values regarding the received
sector power and the detected interference level may change from
one wireless system to another. These values may also vary
depending on the receiver hardware designed.
[0053] Furthermore, the power saving features of the present
invention have been illustrated by using two current modes: a
normal mode and a current saving mode. However, it is possible to
use three or more current modes for different received sector power
levels and interference levels. It is also possible to adjust the
current in a continuous fashion instead of an abrupt fashion.
[0054] Thus, although the invention has been described with respect
to one or more embodiments thereof, it will be understood by those
skilled in the art that the foregoing and various other changes,
omissions and deviations in the form and detail thereof may be made
without departing from the scope of this invention.
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